U.S. Pat. Nos. 3,434,449 and 3,641,965, owned by the same assignee as the present application, disclose electrically controlled switch actuated hydraulically powered extendable and retractable trim/tilt cylinders for vertically trimming or tilting individual outboard motors or stern drives to desired angular positions. Such a cylinder, which is supplied with hydraulic operating fluid from a motor driven pump and responds to actuation of a manually operable three position (off, up, down) electrical switch, effects trim positioning of the drive, as during boat operation, and also raises and lowers the drive for clearance purposes. Trimming is carried out within a trim angle or trim range (defined by full down drive position and some higher trim limit position) and changes the angle of propeller thrust thereby causing the boat bow to raise or lower and enables selection of a proper and more efficient angle for different loads or different water conditions or for getting on plane. Tilting or raising the drive up past the trim range for clearance purposes enables safer shallow water running and facilitates launching or trailing.
When two such trimmable/tiltable drives are mounted side-by-side and used to power the same boat, the power pulses from one drive's propeller interact with the other drive and can cause increased wear of drive components and other problems. The effect of this phenomena is diminished by using an external "tie bar" that mechanically and pivotably connects the housings of the two drives together outside of the boat, while at the same time permitting the drives to be moved horizontally for steering purposes by suitable steering means inside or outside of the boat transom. However, since the tie bar does not telescope or change length in any way, damage can be incurred if the aforedescribed trim/tilt cylinders are operated independently to move one drive up or down for a substantial distance while the other drive is still relatively stationary. Nevertheless, because of mechanical tolerances and clearances in the connection of the tie bar to the drives, relatively small differences in drive angle between the adjacent drives are still possible for trim purposes and do not result in damage. Accordingly, anyone operating a dual drive boat with such an external tie bar has to use extreme care to avoid damage to the drives and/or the tie bar when actuating the trim/tilt cylinders for any purpose.